IGF-I activates PKB and prevents anoxic apoptosis in Achilles tendon cells

Anoxia and apoptosis are both implicated in chronic tendon pathology, however the influence of anoxia on the viability of tendon cells is not known. The objectives of the current study were to (i) investigate the effect of oxygen withdrawal on the viability of porcine Achilles tendon cells (ATCs), and (ii) examine the ability of IGF-I, a factor with known regenerative properties in tendon, to prevent ATC death. Cultured ATCs were enclosed in an anaerobic chamber. The mechanism of cell death was examined by flow cytometry of ATCs double labeled with Annexin-V and propidium iodide (PI). Caspase activity was determined by a fluorometric assay, and nuclear morphology was examined by Hoechst staining. The cell death induced by anoxia was time-dependent, and was characterized by phosphatidylserine exposure on the outer membrane, caspase activation and DNA fragmentation. Death was inhibited by the addition of IGF-I in a dose-dependent manner. The ability of IGF-I to activate the pro-survival PKB pathway in ATCs was inhibited by LY294002, indicating the importance of PI3K in the response of ATCs to IGF-I. These data suggest that cell death induced by lack of oxygen is predominantly apoptotic and can be prevented by pro-survival IGF-I signaling. This mechanism may contribute to the beneficial effect of IGF-I on tendon.